Method for producing phenylalkanes using a combination of two catalysts

ABSTRACT

A process is described for producing phenylalkanes by alkylating at least one aromatic compound using at least one linear olefin containing 9 to 16 carbon atoms per molecule. The alkylation reaction is carried out in the presence of at least two different catalysts used in at least two distinct reaction zones. The selectivity for a monoalkylated products of the catalyst contained in the first reaction zone is lower than that for the catalyst contained in the second reaction zone located downstream of the first in the direction movement of the fluids.

The present invention relates to the field of processes for producingphenylalkanes by alkylating benzene using at least one mono-olefin,usually linear, and generally containing 9 to 16 carbon atoms permolecule. The alkylation reaction is carried out in the presence of atleast two different catalysts, used in at least two distinct reactionzones. The present invention allows the quantity of 2-phenylalkaneisomer produced to be adjusted and modified depending on requirementswhile reducing the proportions of heavy polyalkylated compounds derivingfrom the alkylation reaction. In one non limiting example ofapplication, the phenylalkanes obtained in accordance with the inventionconstitute precursors for formulating detergents after sulphonation, inparticular certain biodegradable detergents.

Currently, bases for biodegradable detergents are largely derived fromlinear alkylbenzenes. Production of that type of compound is increasingsteadily. In addition to their detergent power, one of the principaldesired properties for such compounds, after a sulphonation step, isbiodegradability. To ensure maximum biodegradability, the alkyl groupmust be linear and long and the distance between the sulphonate groupand the terminal carbon of the linear chain must be a maximum. Thus, themost interesting benzene alkylation agents are constituted by linearC₉-C₁₆ olefins, preferably C₁₀-C_(14.)

Linear alkylbenzenes generally obtained by alkylating benzene usinglinear olefin(s) are usually prepared using two known processes. Thefirst process described, for example, in Ullmann's encyclopedia (5^(th)volume A25, page 766) uses hydrofluoric acid as the acid catalyst duringthe benzene alkylation step. The second process described, for example,in Ullmann's encyclopedia (5^(th) volume A25, page 766) uses aFriedel-Crafts type catalyst, generally based on AlCl₃. Those twoprocesses lead to the formation of 2-, 3-, 4-, 5- and 6-phenylalkaneisomers. The principal disadvantage of those processes is connected toenvironmental constraints. The first process, based on the use ofhydrofluoric acid, causes severe problems with safety and with wastetreatment. The second process, based on the use of a Friedel-Crafts typecatalyst, poses problems with discharges deriving from using such acatalyst. In that case, the effluents have to be neutralized with abasic solution at the reactor outlet. Further, the catalyst has to beseparated from the reaction products; in both processes, this isdifficult to carry out.

Such constraints explain the interest in developing a process foralkylating benzene with olefins, and more particularly with linearolefins in the presence of a solid catalyst.

The prior art essentially regards the use of catalysts with geometricselectivity properties leading to improved selectivity for 2- and3-phenylalkanes. Said catalysts with geometric selectivity propertiesare generally constituted by zeolitic compounds as defined in the “Atlasof zeolite structure types” (W M Meier, D H Olson and Ch Baerlocher,4^(th) revised edition, 1996, Elsevier) to which reference should bemade in the present application. United States patent U.S. Pat. No.4,301,317 describes a series of zeolites including cancrinite,gmelinite, mordenite, offretite and ZSM-12. The Applicant's Frenchpatent FR-B-2 697 246 shows that it is possible to use catalysts basedon dealuminated Y zeolite. European patent EP-B1-0 160 144 describes theuse of partially crystalline zeolites, in particular Y zeolites thecrystallinity of which is between 30% and 80% while U.S. Pat. No.5,036,033 describes the use of Y zeolites that are rich in ammoniumcations. U.S. Pat. No. 4,301,316 shows that the nature of the catalysthas a direct influence on the composition of the different phenylalkaneisomers produced. The selectivities for phenylalkane isomers afterreacting 1-dodecene with benzene in the presence of a variety ofcatalysts, as given in the prior art, are shown in Table I. It clearlyshows that for a catalyst with a given structure, the proportion of2-phenylalkane isomer essentially results from the intrinsiccharacteristics of the catalyst. Using an HF catalyst results in aproportion of 20% of 2- phenylalkane, while using ZSM-12 leads to aproportion of 92% of 2-phenylalkane.

TABLE 1 catalyst 2-φ (%) 3-φ (%) 4-φ (%) 5-φ (%) 6-φ (%) ZSM-12 92 8 0 00 mordenite 85 15 0 0 0 offretite 79 14 5 1 1 ZSM-4 57 25 8 5 5 beta 5718 10 7 8 linde L 40 18 16 15 11 ZSM-38 37 19 13 14 16 ZSM-20 51 21 11 98 REY 25 20 18 19 18 HF 20 17 16 23 24 AlC13 32 22 16 15 15

U.S. Pat. No. 6,133,492 discloses a process for producing linearalkylbenzenes resulting in a high selectivity for 2-phenylalkane. Thisprior process uses two reactors in series: the first reactor contains acatalyst based on mordenite zeolite containing fluorine and the secondreactor contains a second alkylation catalyst the selectivity for2-phenylalkane of which is lower than that of the catalyst based onfluorinated mordenite. The second alkylation catalyst is preferablyselected from the group formed by fluorinated silica-alumina, clayscontaining fluorine and aluminium chloride. Even though it results in ahigh selectivity for 2-phenylalkane, this prior art process is notsatisfactory as regards the distribution of the products obtained at theoutlet from the second reactor: dialkylated products and heavy productswith a plurality of linear chains on the benzene ring are produced innon negligible quantities, which limits the proportion of desiredmono-alkylated compounds in the final composition.

The present invention proposes to provide a process for alkylatingaromatic compounds, preferably benzene, using linear olefin(s)containing 9 to 16 carbon atoms per molecule, more particularly 10 to 14carbon atoms per molecule, which can not only allow adjustment of theselectivity for 2-phenylalkane to a desired level but can also increasethe proportion of mono-alkylated products produced, i.e., containingonly a single linear chain on the benzene ring, and as a result lead tothe production of fewer di-alkylated compounds and heavy compounds.

The process of the invention employs at least two distinct reactionzones each containing at least one catalyst, the characteristics ofwhich are given below. The process of the present invention uses atleast two catalysts, the catalysts used in each of said reaction zonesbeing different from each other and the selectivity for monoalkylatedproducts of the catalyst contained in the first reaction zone beinglower than that of the catalyst contained in the second reaction zonelocated downstream of the first in the direction of fluid movement.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE represents the invented process using a serial two beds ofreaction.

Advantageously, at least one of said catalysts contained in saiddistinct reaction zones comprises at least one zeolite. Particularlyadvantageous zeolites for used in the process of the invention areselected from the group formed by zeolites with structure types FAU,MOR, MTW, OFF, MAZ, BEA and EUO. Y zeolite with structure type FAU,mordenite with structure type MOR, ZSM-12 zeolite with structure typeMTW, offretite with structure type OFF, ZSM-4 zeolite with structuretype MAZ and beta zeolite with structure type BEA are particularlypreferred. REY zeolite is a faujasite type zeolite, which is highlyacidic, and can also be used.

In a particular implementation of the invention, in one of the reactionzones a catalyst containing a Y zeolite is used. Clearly, depending onits nature and characteristics, in particular in terms of selectivityfor monoalkylated compounds, of the other catalyst used in combinationwith the catalyst based on Y zeolite and also depending on the desiredproportion of 2-phenylalkane, the catalyst based on Y zeolite willoccupy either the first reaction zone or the second reaction zonelocated downstream of the first zone in the fluid movement direction.The Y zeolite present in one of the catalysts used in any of saidreaction zones is advantageously a dealuminated Y zeolite, with anoverall Si/Al atomic ratio of more than 4, preferably in the range 8 to70 and more preferably in the range 15 to 25, and containing noaluminium species outside the crystalline lattice. Dealuminated Yzeolites and their preparation are known: as an example, referenceshould be made to the disclosure in U.S. Pat. No. 4,738,940.Dealuminated Y zeolite is used as a mixture with a binder or a matrixgenerally selected from the group formed by clays, aluminas, silica,magnesia, zirconia, titanium oxide, boron oxide or any combination of atleast two of said oxides such as silica-alumina or silica-magnesia. Allknown methods for agglomerating and forming are applicable, examplesbeing extrusion, pelletization or drop coagulation. In a particularimplementation, the process of the invention uses a catalyst based on adealuminated Y zeolite, said catalyst generally containing 1% to 100%,preferably 20% to 98% and more preferably 40% to 98% by weight of saiddealuminated Y zeolite and 0 to 99%, preferably 2% to 80%, morepreferably 2% to 60% by weight of a matrix or binder. In a particularimplementation of the invention, the Y zeolite used can also be anacidic HY zeolite characterized by different specifications and inparticular an overall Si/Al atomic ratio of more than 4, preferably inthe range 8 to 70, and more preferably in the range 15 to 25, with asodium content of less than 0.25% by weight, a lattice parameter for theunit cell of less than 24.55×10⁻¹⁰ m, preferably in the range24.21×10⁻¹⁰ m to 24.39×10⁻¹⁰ m, a specific surface area determined usingthe BET method of more than about 300 m²/g, preferably more than about450 m²/g, and a water vapour adsorption capacity at 25° C. for a partialpressure of 3.46 millibars (mbar) of more than about 0.5%, preferablymore than about 3%.

The proportion of extra-lattice aluminium species in the dealuminated Yzeolite is very small or even zero, and so no signal attributable tosuch species can be detected either by ²⁷Al nuclear magnetic resonanceusing magic angle rotation, nor by infrared spectroscopy in the hydroxylgroup region. More quantitatively, the ratio of the intensity of thesignals corresponding to extra-lattice (ex-framework) aluminium speciesto the intensity of signals corresponding to the aluminium species inthe framework is less than 0.05, regardless of the characterizationtechnique used.

The overall Si/Al atomic ratio is generally measured by chemicalanalysis. When the quantity of aluminium is low, for example less than2%, an atomic adsorption spectrometric assay method is preferably used.

The lattice parameter can be calculated from the X ray diffractiondiagram, using the method described in American Standard ASTM D 3942-80.to carry out this calculation, the crystallinity of the product shouldbe sufficiently high.

The specific surface area is, for example, determined by measuring thenitrogen adsorption isotherm at the temperature of liquid nitrogen andcalculated using the conventional BET method. Before measurement, thesamples are pre-treated at 500° C. in a stream of dry nitrogen.

Water take-up percentages (or water vapour adsorption capacity) aredetermined, for example, using a conventional gravimetric apparatus. Thesample is pre-treated at 400° C. under low vacuum, then heated to astable temperature of 25° C. Water is then admitted at a pressure of3.46 mbar, corresponding to a P/P₀ ratio of about 0.10 (ratio betweenthe partial pressure of water admitted into the apparatus and thesaturated vapour pressure of water at 25° C.).

Y zeolites are generally produced from a NaY zeolite using a suitablecombination of two basic treatments: a) a hydrothermal treatment whichcombines temperature and water vapour partial pressure, and b) an acidtreatment preferably carried out using a strong concentrated mineralacid. Generally, the NaY zeolite from which the Y zeolite is preparedthat is used in the process of the invention has an overall Si/Al atomicratio in the range about 1.8 to 3.5; it is convenient to first reducethe sodium content to less than 3% by weight, preferably to less than2.5%. The sodium content can be reduced by ion exchange of the NaYzeolite with ammonium salt solutions (nitrate, sulphate, oxalate, etc.),with an ammonium concentration between 0.01 and 10 N, at a temperaturein the range 10° C. to 180° C. (optionally with exchange underautogenous pressure) for a period of more than about 10 minutes. The NaYzeolite also generally has a specific surface area in the range about750 to 950 m²/g.

In a further particular implementation of the invention, a catalystcontaining a mordenite zeolite is used in one of the reaction zones.Clearly, depending on its nature and characteristics, in particular itsselectivity for monoalkylated compounds, the other catalyst used incombination with the catalyst based on mordenite zeolite and alsodepending on the desired proportion of 2-phenylalkane, the catalystbased on mordenite zeolite will occupy either the first reaction zone orthe second reaction zone located downstream of the first zone in thefluid movement direction. The mordenite zeolite present in one of thecatalysts used in any of said reaction zones is advantageously a nonfluorinated mordenite zeolite. It generally has an overall Si/Al atomicratio in the range 6 to 100, preferably in the range 15 to 60 and morepreferably in the range 20 to 50, with a sodium content of less than1000 ppm by weight, preferably less than 500 ppm, a microporous volume,measured by adsorption of nitrogen at 77K in a nitrogen partial pressureof 0.19, of more than 0.160 cm³ (liquid)/g, preferably more than 0.180cm³ (liquid)/g. In a first stage, preparing the catalyst based on azeolite with structure type MOR, preferably mordenite zeolite, consistsof eliminating the major portion of the sodium cations present in saidzeolite and replacing them with protons and then in a second stageoptimizing the overall Si/Al and framework ratios. To eliminate themajor portion of the sodium cations, it is possible to carry out one ormore series of exchanges in solutions of ammonium salts (ammoniumchloride, nitrate or sulphate, for example) in a solution with aconcentration in the range 0.01 to 15 N or in solutions of a variety ofacids (HCl, H₂SO₄, HNO₃ of low normality) at a temperature in the range10° C. to 180° C. Said exchange can optionally be carried out underautogenous pressure for a period of more than about 10 minutes.

To obtain the desired overall and framework Si/Al ratios, dealuminationtechniques that are known to the skilled person can be used, for exampledirect acid attack of the sodium form of the mordenite (NaMOR) partiallyexchanged or not partially exchanged with H⁺ or NH₄ ⁺ ions (HMOR orNH₄MOR respectively), calcining of the HMOR or NH₄MOR form optionally inthe presence of steam preferably being followed by a chemical treatmentof the acid attack type. Acid attack consists of at least one treatmentin acid solutions of various natures (HCl, HNO₃, H₂SO₄, HF etc) attemperatures in the range 50° C. to 150° C. (optional attack underautogenous pressure). The acid concentration s are in the range 0.5 to15 N, preferably in the range 5 to 12 N. The volume ratios of solutionper weight of dry solid are in the range 3 to 20 cm³/g, advantageouslyin the range 3 to 7 cm³/g. The treatment period is at least 10 minutes.To achieve the desired specifications, a limited number of acid attackscan be carried out under severe conditions or a larger number of attackscan be carried out under moderate conditions. Direct acid treatment on amordenite can also eliminate the major portion of the sodium cations andthus avoid an initial cation exchange step. Heat treatment in thepresence of steam normally consists of calcining carried out at atemperature of more than 350° C., preferably more than 500° C., for aperiod of at least 10 minutes, in an atmosphere containing at least 1%steam, preferably at least 10% steam. The acid attack which optionallyfollows calcining is carried out under the same conditions as the acidattack described above.

According to the present invention, the prepared mordenite can be usedalone or as a mixture with a binder or a matrix generally selected fromthe group formed by clays, aluminas, silica, magnesia, zirconia,titanium oxide, boron oxide and any combination of at least two of thesecompounds, preferably silica-alumina or silica-magnesia. All knownmethods for agglomeration and forming are applicable, such as extrusion,pelletization, drop coagulation or spray drying. In a particularimplementation of the invention, a catalyst based on a mordenite isused, said catalyst generally containing 1% to 100%, preferably 20% to98% and more preferably 40% to 98% by weight of said mordenite and 0 to99%, preferably 2% to 80% and more preferably 2% to 60% by weight of amatrix or a binder.

To carry out the process of the invention, it may also be highlyadvantageous to use in each of said distinct reaction zones at least onecatalyst containing at least one zeolite (zeolitic catalyst). Inaccordance with the invention, the zeolites present in each of thezeolitic catalysts differ from each other in their structure type and/orin the chemical composition of their crystalline framework. As anexample, it is possible to use two zeolitic catalysts each containing azeolite with a different structure type. It is also possible to use twozeolitic catalysts each containing a zeolite with an identical structuretype but with a different chemical composition for the crystallineframework, i.e., with a different Si/Al ratio, for example, so that eachof the zeolitic catalysts has a different selectivity for monoalkylatedcompounds, for example after a different maturation treatment. Anycombination of two zeolitic catalysts differing by their structure typeand/or a chemical composition of the crystalline framework for thezeolites used and in which the selectivity for monoalkylated compoundsof the catalyst used in the first zone is lower than that of thecatalyst used in the second zone can be envisaged for carrying out theprocess of the invention to obtain the desired selectivity for2-phenylalkane and an optimum selectivity for monoalkylated compounds.In this implementation of the invention, in which at least two zeoliticcatalysts are combined, a particularly preferred combination is acombination of a catalyst based on a zeolite with structure type FAU, inparticular Y zeolite, and a catalyst based on a zeolite with structuretype MOR, in particular mordenite zeolite, the zeolite with structuretype FAU being contained in the first catalyst, i.e., in the catalystpresent in the first reaction zone, and the zeolite with structure typeMOR being contained in the second catalyst, i.e., in the second reactionzone located downstream of the first in the direction of fluid movement.The Y and MOR zeolites contained in each of the zeolitic catalysts havesimilar physico-chemical properties to those described above. By meansof this combination of Y and mordenite zeolites, it is possible toadjust the proportion of 2-phenylalkane at the outlet from the processbetween about 25% by weight and about 85% by weight.

The process of the present application can be carried out in a singlereactor, generally a fixed bed reactor, in which the reaction zonescontaining the catalysts are located, or it can be carried out inreactors in series, each containing a single catalytic zone containingone catalyst type. This second configuration will usually be preferredas it can generally better accommodate the properties and optimumreaction conditions associated with each catalyst, for example byadjusting the temperatures of the two reactors independently.

In one implementation of the process of the invention, the olefin(s)is/are mixed with the aromatic compound(s) upstream of the firstreaction zone.

In a further preferred implementation of the process of the invention, afirst fraction of the olefin(s) is mixed with the aromatic compoundsupstream of the first catalytic zone and a second fraction of theolefin(s) is mixed with at least a portion of the effluents from thefirst reaction zone. Preferably, the quantity of olefin(s) contained insaid first fraction is such that substantially all of said olefin(s) isconsumed in the first reaction zone.

In general, the alkylation reaction is followed by at least one step forseparating excess reactants. It is also advantageously followed by atleast one step for separating the monoalkylated compounds from thereaction.

In a non limiting application of the process of the invention, benzeneis reacted with a feed comprising at least one linear olefin containing9 to 16 carbon atoms per molecule, preferably 10 to 14 carbon atoms permolecule, the feed possibly containing paraffins. All of the benzene canbe introduced into the inlet to the first reaction zone containing thefirst catalyst, the mixture containing the linear olefins can beintroduced in its entirety into the inlet to the first zone, orpreferably fractionated into at least two portions, one being introducedto the inlet to the first catalyst zone, the other being introduced tothe inlet to the second zone, located downstream of the first in thedirection of fluid flow. When a single reactor comprising a plurality ofreaction zones is used, side injection can be carried out into thereactor, for example, into a zone located between two reaction zones.

At the outlet from the reactor or reactors, i.e., the zone containingthe second reactor, the product obtained is generally fractionated torecover separately a first fraction comprising unconverted benzene, asecond fraction comprising at least one unconverted linear C₉-C₁₆ olefin(preferably C₁₀-C₁₄) and the paraffins that may have initially beenpresent in the feed, a third fraction comprising 2-, 3-, 4-, 5- and6-phenylalkanes and a fourth fraction comprising at least onepolyalkylbenzene (or polyalkylbenzene fraction), which can optionally berecycled at least in part to one of the two reaction zones where itreacts with benzene in contact with the catalyst present in thecatalytic zone concerned, in order to be at least partiallytransalkylated (transalkylation reaction) and a mixture of 2-, 3-, 4-,5- and 6-phenylalkanes is recovered.

Similarly and preferably, the second fraction comprising at least oneunconverted linear C₉-C₁₆ (normally C₁₀-C₁₄) olefin is recycled at leastin part to one of the two reaction zones.

The operating conditions applied to the two reaction zones are, ofcourse, selected by the skilled person as a function of the structure ofthe catalyst, the total pressure being substantially the same (with theexception of pressure drops) for the two reaction zones. The tworeaction zones are operated at a temperature that is normally less than400° C., preferably less than 300° C. and more preferably less than 250°C. and at a pressure of 1 to 10 MPa, with a flow rate of liquidhydrocarbons (space velocity) of about 0.5 to 50 volumes per volume ofcatalyst per hour and with a benzene/(C₉-C₁₆ linear olefin) mole ratioin the range 1 to 20. Different temperatures can, of course, be employedin the two reaction zones, in the event when two separate reactors areused.

A particular implementation of an apparatus for carrying out the processof the invention is described in relation to the accompanying figure. Itis not limiting in scope.

Fresh benzene arriving via a line 1 is mixed with benzene from the headof a first fractionation column 9 (line 10). This feed constituted bybenzene is mixed with a stream comprising linear C₉-C₁₆ olefins,preferably C₁₀-C₁₄ linear olefins, and mainly C₁₀-C₁₄ paraffins (line2). The overall mixture obtained constitutes the feed to an alkylationreactor 6. Said feed initially traverses a heat exchanger 3 where it ispre-heated by indirect heat exchange with an effluent from alkylationreactor 6. After passing through heat exchanger 3, the feed is sent toalkylation reactor 6 via a line 4. The alkylation reactor 6 ischaracterized in that it comprises two distinct reaction beds A and B,each containing a different catalyst. A second mixture constituted by atleast linear C₉-C₁₆ olefins, preferably C₁₀-C₁₄ linear olefins,accompanied by mainly C₁₀-C₁₄ paraffins is introduced via line 5directly into reactor 6, the injection point being located between thetwo catalyst beds A and B. At the outlet from reactor 6, the effluent issent via line 7 to heat exchanger 3 then via a line 8 to a firstfractionation column 9. At the head of said first fractionation column9, the majority of the excess benzene that has not reacted is extractedand recycled via a line 10. A fraction is recovered from the bottom ofthis first fractionation column 9 and sent to a second fractionationcolumn 12. Linear C₉-C₁₆ olefins, preferably C₁₀-C₁₄, that have not beentransformed, and the paraffins initially present in the feed are mainlyrecovered from the head of this second fractionation column 12. At leasta portion of this effluent can be recycled to the line supplying benzeneto reactor 6. A mixture is recovered from the bottom of this secondfractionation column 12, which is sent via a line 14 to a thirdfractionation column 15. A mixture of 2-phenylalkane, 3-phenylalkane,4-phenylalkane, 5-phenylalkane and 6-phenylalkane is mainly recoveredfrom the head of this third fractionation column 15 and sent to storagevia a line 16. Dialkylbenzenes are mainly recovered from the bottom ofthis third fractionation column 15 via a line 17.

Examples 1 to 6 below do not limit the scope of the invention. They aregiven by way of illustration to provide the skilled person with a betterunderstanding of the present invention.

EXAMPLE 1 Preparation of Catalyst A Based on Y Zeolite

The starting material was a NaY zeolite with formula NaAlO₂(SiO₂)_(2.5).This zeolite underwent 5 successive exchanges in ammonium nitratesolutions at a concentration of 2M, at a temperature of 95° C. for aperiod of 2 hours and with a (volume of solution/weight of zeolite)ratio of 8 cm³/g. The sodium content in the NH₄Y zeolite obtained was0.9% by weight. This product was rapidly introduced into a furnacepre-heated to 770° C. and left for 4 hours in a static atmosphere. Thezeolite then underwent an acid treatment under the following conditions:the ratio between the volume of 3 N nitric acid and the weight of solidwas 0.9 cm³/global; the temperature was 95° C. and the treatment periodwas 3 hours. A further treatment was then carried out under the sameconditions, but with a 0.5 N nitric acid solution. The zeolite obtainedhad a sodium content of 0.1% by weight and a Si/Al atomic ratio of 24.The zeolite was formed by extrusion with alumina (80% Y zeolite and 20%alumina). The extrudates were then dried and calcined at 550° C.

EXAMPLE 2 Preparation of Catalyst B Based on Mordenite Zeolite (MOR)

The starting material was a mordenite zeolite in its sodium form withchemical formula (anhydride form) NaAlO₂(SiO₂)_(5.1) and a sodiumcontent of 5% by weight. 100 grams of this powder was heated underreflux to 100° C. for 2 hours in a solution of 4M ammonium nitrate witha (volume of solution/weight of zeolite) ratio of 4 cm³/g. This cationexchange operation was repeated 3 times. The sodium content in theNH₄MOR zeolite was about 500 ppm (parts per million). The zeolite thenunderwent an acid attack using an aqueous 4.5N nitric acid solution: thezeolite was heated under reflux in this aqueous solution for 2 hourswith a (volume of HNO₃/weight of zeolite) ratio of 4 cm³/g. After thistreatment, the zeolite was washed with demineralized water. Themordenite obtained had a Si/Al atomic ratio of 40 and a sodium contentof 20 ppm by weight. It was then mixed with an alumina gel (80% byweight mordenite and 20% by weight alumina gel). The mixture obtainedwas formed into extrudates with a diameter of about 1.8 mm by passingthrough a die. The extrudates were then oven dried at 120° C. overnightand calcined in dry air at 550° C.

EXAMPLE 3 Alkylation of Benzene by 1-dodecene- in the Presence ofCatalyst A Based on Y Zeolite (Not in Accordance With the Invention)

A reactor containing 50 cm³ of catalyst A in the form of extrudatesprepared as described in Example 1 was used.

The operating conditions for alkylating benzene by 1-dodecene were asfollows:

-   -   temperature: 135° C.;    -   pressure: 4 MPa;    -   HSV=1 h⁻¹ (cm³ (benzene+1-dodecene) feed/cm³ of catalyst/hour);    -   Benzene/1-dodecene mole ratio: 5.5.

A feed was prepared containing 72% by weight of benzene and 28% byweight of 1-dodecene. The results obtained are shown in Table 2.

TABLE 2 conversion of 1-dodecene (%) 99.2 Composition of productobtained (wt %) 2-phenylalkane 26.2 3-phenylalkane 21 4-phenylalkane18.9 5-phenylalkane 11 6-phenylalkane 10.9 didodecylbenzene 11 heavyresidue 1

The proportion of 2-phenylalkane in the mixture constituted by2-phenylalkane, 3-phenylalkane, 4-phenylalkane, 5-phenylalkane and6-phenylalkane was 29.5%. The monoalkylated products represented 88% byweight of the total composition from the alkyl reaction carried out witha catalyst based on a Y zeolite.

EXAMPLE 4 Alkylation of Benzene by 1-dodecene- in the Presence ofCatalyst B Based on Mordenite (Not in Accordance With the Invention)

Again, a reactor containing 50 cm³ this time of catalyst B in the formof extrudates prepared as described in Example 2 was used. The testdescribed in Example 3 was carried out under the same operatingconditions and with the same feed. The results obtained are shown inTable 3.

TABLE 3 conversion of 1-dodecene (%) 98.7 Composition of productobtained (wt %) 2-phenylalkane 77.2 3-phenylalkane 11 4-phenylalkane 1.55-phenylalkane 0.2 6-phenylalkane 0 didodecylbenzene 9.6 heavy residue0.5

The proportion of 2-phenylalkane in the mixture constituted by2-phenylalkane, 3-phenylalkane, 4-phenylalkane, 5-phenylalkane and6-phenylalkane was 85.9%. The monoalkylated products represented 89.9%by weight of the total composition from the alkyl reaction carried outwith a catalyst based on mordenite.

EXAMPLE 5 (In Accordance With the Invention): Alkylation of Benzene by1-dodecene- in Two Reactors Mounted in Series

An apparatus comprising two distinct reactors was used. In accordancewith the process of the present invention, 30 cm³ of catalyst A based onY zeolite was used in a first bed in the first reactor, and 20 cm³ ofcatalyst B based on mordenite was used in a second bed in the secondreactor, the selectivity for monoalkylated products of catalyst A beinglower than that of catalyst B. A feed was prepared containing 84% byweight of benzene and 16% by weight of 1-dodecene. This feed wasinjected into the inlet to the first reactor containing catalyst A. Pure1-dodecene was also injected between the two reactors. Benzene wasinjected into the inlet to the first reactor at a flow rate of 34.5cm³/h and 1-dodecene at a flow rate of 9.3 cm³/h. All of the effluentleaving the first reactor and 1-dodecene at a flow rate of 6.2 cm³/hwere injected into the inlet to the second reactor. The first reactorthus functioned with a benzene/1-dodecene flow rate of 10.5.

The experimental conditions were as follows:

-   -   temperature of the two reactors: 135° C.;    -   pressure: 4 MPa;    -   overall HSV over the two reactors: 1 h⁻¹ (expressed as cm³ of        feed (benzene+1-dodecene) /cm³ of catalyst/hour);

The results obtained are shown in Table 4. The compositions indicatedare those determined at the outlet from the second reactor.

TABLE 4 conversion of 1-dodecene (%) 99.1 Composition of productobtained (wt %) 2-phenylalkane 49.9 3-phenylalkane 17.6 4-phenylalkane11.1 5-phenylalkane 6.9 6-phenylalkane 7 didodecylbenzene 7.1 heavyresidue 0.4

The proportion of 2-phenylalkane in the final mixture constituted by2-phenylalkane, 3-phenylalkane, 4-phenylalkane, 5-phenylalkane and6-phenylalkane was 54%. The monoalkylated products represented 92.5% byweight of the total composition from the alkylation reaction.

It can also be seen that using the two catalysts substantially increasedthe selectivity for monophenylalkanes (monoalkylated products) byreducing the quantity of dialkylated compounds and heavy polyalkylatedcompounds.

EXAMPLE 6 (Comparative): Alkylation of Benzene by 1-dodecene- in TwoReactors Mounted in Series

A combination of two catalysts was used: the catalyst used in the firstbed was catalyst B based on mordenite zeolite as described above; thecatalyst used in the second bed was a catalyst based on silica-aluminasold by Condea under the trade name Siralox 40. To determine theselectivity of the catalyst based on silica-alumina for monoalkylatedproduct when it is used to alkylate benzene by 1-dodecene, a testsimilar to that described in Example 3 was carried out under the sameoperating conditions. After the reaction, the 1-dodecene conversion was100% and the proportion of monoalkylated products in the mixtureconstituted by the monoalkylated compounds, dialkylated compounds andheavy residues was 68.5%. The selectivity for monoalkylated products ofthe, catalyst based on silica-alumina was thus lower than that forcatalyst B based on mordenite used in the first catalytic bed.

To carry out the reaction for alkylating benzene by 1-dodecene in thepresence of two catalysts as described above, an apparatus comprisingtwo distinct reactors was used. 30 cm³ of catalyst B based on mordenitewas used in a first bed in a first reactor, and 20 cm³ of Siralox 40(silica-alumina) catalyst was used in a second bed in a second reactor.

A feed was prepared containing 84% by weight of benzene and 16% byweight of 1-dodecene. This feed was injected into the inlet to the firstreactor containing catalyst B. Pure 1-dodecene was also injected betweenthe two reactors. Benzene was injected into the inlet to the firstreactor at a flow rate of 34.5 cm³/h along with 1-dodecene at a flowrate of 9.3 cm³/h. All of the effluent leaving the first reactor wasinjected into the inlet to the second reactor along with 1-dodecene at aflow rate of 6.2 cm³/h. Thus, the first reactor functioned with abenzene/1-dodecene mole ratio of 10.5.

The experimental conditions were as follows:

-   -   temperature of the two reactors: 135° C.;    -   pressure: 4 MPa;    -   overall HSV over the two reactors: 1 h⁻¹ (expressed as cm³ of        feed (benzene+1-dodecene) /cm³ of catalyst/hour);

The results obtained are shown in Table 5. The compositions indicatedare those determined at the outlet from the second reactor.

TABLE 5 conversion of 1-dodecene (%) 100 Composition of product obtained(wt %) 2-phenylalkane 46.3 3-phenylalkane 15.2 4-phenylalkane 10.05-phenylalkane 6.2 6-phenylalkane 3.5 didodecylbenzene 15.6 heavyresidue 3.2

The proportion of 2-phenylalkane in the final mixture constituted by2-phenylalkane, 3-phenylalkane, 4-phenylalkane, 5-phenylalkane and6-phenylalkane was 57%. The monoalkylated products represented 81.2% byweight of the total composition from the alkylation reaction.

The combination of the two catalysts disposed in such a manner that theselectivity for monoalkylated products of the catalyst in the firstreactor was higher than that of the catalyst in the second reactorallowed the amount of 2-phenylalkane to be adjusted to a value of closeto that obtained by a combination of two catalysts in accordance withthe process of the invention, i.e., disposed so that the selectivity formonoalkylated products of the catalyst occupying the first reactor waslower than that of the catalyst in the second reactor. In contrast, theprocess of the invention resulted in a substantial improvement in theyield of monoalkylated products (92.5% by weight as opposed to 81.2% byweight) to the detriment of the production of di-alkylated compounds andheavy polyalkylated compounds (7.5% as opposed to 18.8% in thecomparative example).

1. A process for producing phenylalkanes comprising alkylating at leastone aromatic compound by at least one linear olefin containing 9 to 16carbon atoms per molecule carried out in the presence of at least twodifferent catalysts and used in at least two distinct reaction zones,the selectivity for monoalkylated products of the catalyst contained inthe first reaction zone being lower than that of the catalyst containedin the second reaction zone located downstream of the first reactionzone in the direction of fluid movement.
 2. A process for producingphenylalkanes according to claim 1, in which at least one of saidcatalysts contained in said reaction zones comprises at least onezeolite.
 3. A process for producing phenylalkanes according to claim 2,in which the zeolite is selected from the group formed by consisting ofzeolites with structure types FAU, MOR, MTW, OFF, MAZ, BEA and EUO.
 4. Aprocess for producing phenylalkanes according to claim 3, in which thezeolite is a zeolite with structure type FAU.
 5. A process for producingphenylalkanes according to claim 4, in which the zeolite is a Y zeolite.6. A process for producing phenylalkanes according to claim 3, in whichthe zeolite is a zeolite with structure type MOR.
 7. A process forproducing phenylalkanes according to claim 6, in which the zeolite is amordenite zeolite.
 8. A process for producing phenylalkanes according toclaim 1, in which the two catalysts are zeolitic catalysts.
 9. A processfor producing phenylalkanes according to claim 8, in which the zeolitescontained in each of the different zeolitic catalysts differ from eachother in their structure type and/or in the chemical composition oftheir crystalline framework.
 10. A process for producing phenylalkanesaccording to claim 8, in which the zeolitic catalyst of the firstreaction zone contains a Y zeolite and the zeolitic catalyst in thesecond reaction zone contains a mordenite zeolite.
 11. A process forproducing phenylalkanes according to claim 1, in which the olefin ismixed with the aromatic compound upstream of the first reaction zone.12. A process for producing phenylalkanes according to claim 1, in whicha first fraction of the olefin is mixed with the aromatic compoundupstream of the first catalytic zone and in which a second fraction ofthe olefin is mixed with at least a portion of the effluents from thefirst reaction zone.
 13. A process for producing phenylalkanes accordingto claim 12, in which the quantity of olefin contained in said firstfraction is such that substantially all of the olefin is consumed in thefirst reaction zone.
 14. A process for producing phenylalkanes accordingto claim 1, in which said alkylation reaction is followed by at leastone step for separating the excess reactants.
 15. A process forproducing phenylalkanes according to claim 1, in which said alkylationreaction is followed by at least one step for separating monoalkylatedcompounds deriving from the reaction.
 16. A process for producingphenylalkanes according to claim 1, in which the linear olefin is anolefin containing 10 to 14 carbon atoms per molecule.
 17. A process forproducing phenylalkanes according to claim 1, in which the linear olefinis 1-dodecene.
 18. A process according to claim 1, further comprisingsuiphonating the obtained phenylalkane to produce a detergent.